Lightning-arrester



(No Model.)

B THOMSON. LIGHTNING ARRESTER. No. 495,853. Patented Apr. 18, 1893.

Fus-1 5:12.

UNITED STATES PATENT OFFICE.

ELIHU THOMSON, OF SVVAMPSCOTT, MASSACHUSETTS, ASSIGNOR TO THE THOMSONTIOUSTON ELECTRIC COMPANY, OF CONNECTICUT.

LIGHTNING-ARRESTER.

SPECIFICATION forming part of Letters Patent No. 495,853, dated April 18, 1893.

Application filedPebrnary 15,1892. Serial No. 421,501. (No model.)

To all whom it may concern.-

Be it known that I, ELIHU THOMSON, a citizen of the United States, residing at Swampscott, county of Essex, State of Massachusetts, have invented certain new and useful Improvements in Lightning-Arresters and Discharge-Protectors, of which the following is a specification.

The principal distinguishing feature of the present invention is the manner in which a lightning or other high potential discharge is enabled to pass over a discharge path interrupted by spark gaps, byinducing from such discharge in a proper circuit a secondary discharge or discharges of greatly increased potential, such as will leap a space between electrodes placed at a considerable distance apart, or leap a succession of electrodes placed at such a distance apart that the normal potential of the line is unable to maintain a continued arc thereat, thus avoiding permanently grounding the line current, a difliculty which always has to be guarded against, and which is especially liable to occur when the line current is of itself of considerable potential. This secondary discharge gives rise to a series of sparks jumping across the discharge space, which breaks down the dielectric so that the main discharge will follow even though it might not otherwise, of itself form an arc across the terminals. The manner in which this result is secured will be understood from the drawings, in which Figure 1 is a diagrammatic view of the invention. Fig. 2 is a sectional view of a casing containing oil in which the coils areimmersed. Fig.3isa diagram showing the mode of coupling up the secondary coils in circuit, and Figs. 4 and 5 illustrate different forms of are disrupting devices which under certain conditions it is desirable to use.

static discharge does leap the intervening spaces. The plate P is connected to the earth plate E, P is an intermediate plate, and P is connected to the line L to be protected through the primary of an induction coil A, A made of a few turns of highly insulated wire. The secondary consists of due wire coils S, S surrounding the primary turns, which coils respectively have one end connected to plate P and to plate P, while the other ends of both coils are connected to the intermediate plate P through condensers C, C of moderate capacity and high insulation resistance, all as will be readily traced on Fig. 1. Shunting the gaps between and connected to the plates P, P is a condenser of somewhat larger capacity as at K.

The action of the apparatus is as follows: Suppose the line L, to which it is connected, to be a high potential circuit, such as would maintain an arc across the ordinary lightning arrester plates when unprovided with are rupturing appliances, but which will not maintain an arc across the gaps between the plates P and P, since as has been explained these are of greater width than is usual in such devices. Now let a static discharge pass through the line L tending to go to earth, a quick impulse of current passes through the coarse wire primary charging the condenser K there will at once be an induction of great energy set up in the secondary fine wire coils S, S, which will charge the condensers C, C and cause thin sparks to leap across the gaps between plates P, P and P, P. These thin induced sparks will cause condenser K to discharge instantly as the dielectric has been broken down by the sparks. A snap and somewhat considerable discharge will appear between the plates, and for a moment this discharge will act as a good connection to earth and discharge the line L of any static potential. The distance,

however, between the plates is so great that the normal potential of the line cannot maintain arcs thereat and so become grounded. The number of turns in the fine wire coils S, S and the capacity ofthe condensers C, C and K must be adjusted to give the spark as This adjustment stated between the plates.

once obtained need not be changed. The especial purpose of the small condensers O, 'O' is to guard against any short-circuiting of the line current between plates P and I? through the secondary coils S, S. If the resistance of these coils be so high that any such leakage, in case the condensers be omitted, does no harm then the condensers may be dispensed with. It is obvious that the condensers may be placed anywhere in the circuit of coils S, S and need not necessarily be in the position shown. On account of the very high potential developed in the coils S, S, even when a very moderate length of wire is used, it is well to immerse them in a good dielectric fluid, like oil. For this purpose, as shown in Fig. 2, a small vat Q may be provided containing oil, and the inner coarse coil forming the primary will then be put in a glass tube around which the finer coils S,

S are wound, the whole being immersed in the oil so as to be fairly free from static discharges or short-circuiting. I find that a single layer of fine wire in the coils S, S will often be sufficient. In case more layers are .used the windings should be carefully arranged so that the discharge does not shortcircuit between the layers.

In Fig. 3 the manner of coupling up the secondary coils in circuit with the different arrester plates is shown separately. Itis the 1 same as in Fig. 1, but in this figure the condenser K and the primary coils acting inductively on. the coils S, S are omitted for the sake of clearness. Here also the discharge plates are shown tapered, thereby forming diverging discharge spaces between them, such as will easily enable an arc to become extended or lengthened and break.

Though in many cases the arrangement described will do away with the necessity for special arc rupturing devices, still the invention does not preclude the application of any of the usual means of blowing out or distorting an are at the discharge plates. For example, a magnet M, seen in Fig. 4, may be used, the poles of which overlap the discharge gaps.

As shown in Fig. 5 an upward draft of air or an air jet may be allowed to blow on the spaces between the arrester plates, and in fact a portion of the current itself may be made to set up a draft in properly constructed chimneys O, O by heating or resistance coils R located therein, and through which the current is passed. The addition of such appliances will be useful when dealing with very high potentials in which case the discharge spaces, in order to properly extinguish the arc, would otherwise have to be made too great, and thus excessive potential in the fine wire coils S, S would be required in order to spark across them, and thus start the discharge.

What I claim as new, and desire to secure by Letters Patent, is-

1. The combination in a lightning arrester or discharge protector, of a discharge path around the apparatus to be protected comprising a protective spark gap or set of gaps, with means for breaking down the dielectric in the gap and thereby enabling the passage of currents of lower potential than that by which the dielectric is first broken down, as set forth.

2. The combination of a protective spark gap or set of gaps, and means controlled by the discharge current for breaking down the dielectric in the gap by the momentary exhibition thereat of a potential or electric strain greater than that which would be due to the discharge itself, as set forth.

3. The combination of a protective spark gap or set of gaps, with means for bridging such gap or gaps to allow the passage of a dis charge by inducing over the same an electric strain or potential greater than that which would be due to the discharge itself, as set forth.

4. The combination of arrester or discharge terminals separated by a protective spark gap or set of gaps, such that the line potential will not maintain an arc thereat, with an induction device energized by the discharge and acting to break down the dielectric at the gap by inducing across the same an electric strain or potential considerably greater than that which would be due to the arc itself.

5. In a discharge protector or arrester for lightning or static discharges an induction coil the primary of which is in a connection from line to earth, and the secondary of which has its terminals arranged to deliver their static discharges between the discharge points or plates of the arrester for facilitating the passage of the main discharge over such arrester.

6. In a lightning arrester or discharge protector, discharge plates widely separated so as not to be in themselves distinctively protective from static discharges of moderately high potential, in combination with induction apparatus for causing high potential discharges to leap the spaces between the plates and to be followed by the main body of the static discharge to be carried off.

7. In a lightning arrester or discharge protector a set of discharge plates separated a considerable interval such as will not allow arcs to he maintained thereat between line and earth by the normal line potential, a condenser around such discharge plates, an earth connection for the discharge plates, and a primary coil in series with the condenser,with a secondary coil or coils in which is induced a high potential discharge for leaping the spaces between the arrester plates and thereby momentarily earthing the total discharge.

8. In a lightning arrester or discharge protector, the combination of discharge terminals separated by a spark gap or gaps to be leaped by the discharge, an initial path for a portion of the discharge around such plates, and induction apparatus in inductive relation to the discharge path, and connected up in circuit so that a discharge induced in the secondary each of which coils is placed a condenser of of such apparatus leaps the spark gap first high insulation resistance,substantially as set and thus enables the main discharge to folforth.

low, as set forth. In testimony whereof I have hereto set my 5 9. A lightning arresteror discharge protechand this 12th day of February, 1892.

tor for discharge plates connected to earth and to line respectively, and one or more interme- ELIHU THOMSON diate plates connected in circuit with induc- Witnesses: tion apparatus of high potential adapted to be JOHN W. GIBBONEY,

1o energized by the discharge, in the circuit of BENJAMIN B. HULL. 

